I have a 98 mustang. I just replaced thermostat and gasket. Now all of sudden my temp rises and goes back down. And occasionally floats from the N to the O of normal. And sometimes will go all the way to the A and go straight back down. I am so confused?! And in the process of all this my heat will sometimes cut out?! I need some help :P

 

mmmm....I was going to say maybe your gauge is broken till you said that your heat cuts out. I guess its possible that it could be two separate issues. welcome to the site, hopefully someone will be able to help you!

 

You guys.. Is it a possibility I have air in my hoses near my radiator?

 

The cooling system may have some air in it. Loosen the rad cap, get the car up to op temp, remove the rad cap (no problem since it was loose) and top off the rad with coolant.

 

If it's a 3.8 l it's probably the head gaskets, if you were having the same problem before you changed the thermostat.

 

I agree with John air bubble in there somewhere and your fluid is probably a little low.

 

My car didnt do this before I changed the thermostat. It's doing it like a week after I changed my thermostat? Ughh..

 

is the rad reservoir full or at least up to the full line when your car is cold?

 

yea its full and is really clean

 

Jack the front of the car up & put it on jack stands. Want cap at highest point.

Remove main radiator cap. (Cold)

Put the heater on full hot.

Run engine till all air burps from the system. T-stat must fully open.

Have extra fluid to add as needed & fill right to the top so expansion tank will pick it up.

 

As stated, probably air. I know in my truck when I get an air bubble, everytime it goes past the temp sender, my gauge turns off and then after it passes comes back to life. Also, just remember it's possible you bought a bum thermostat.

And another thing is that by draining all the coolant, doing your work, then refilling you probably worked up any sediment in that system and it's floating around. I just needed a new radiator 6 weeks ago, and before that my temp was all over the place. One day it'd run in the N-O range, next day the R-M-A range, couple times hit the L and then by then I was trying to figure out what was wrong.

 

Did it ever over heat on you? Because while the Temp is going up and down it'll go to the L but it wont over heat. And while its going up if i put it in Neatral and drop it back down in drive the temp will go back down usually.. I'd hate to buy new radiator and that not be the problem. Is it possible that my sending unit went out? ? ErrR I just dont know what it is

 

+1. You need to burp the air bubble out of the radiator.